While various eye disorders are related to elevated pressure within the eye, glaucoma is perhaps the most prevalent. Glaucoma is characterized by loss of optic nerve fibers, visual field loss (e.g., tunnel vision) and, if not effectively treated, by partial or total blindness of the affected eye.
While many types of glaucoma exist, most types are caused by chronic elevation of the intraocular pressure. The elevated pressure affects all parts of the eye. However, due to the specific anatomical location of the optic nerve and the delicate nature of the nerve tissue, it generally suffers the brunt of the disease. The loss of the nerve tissue, which typically occurs very slowly, results in an deformation of the nerve known as "cupping." As one might guess, a cupped nerve looks like it has been cupped out or excavated. While the effect of cupping on the visual function is directly related to the loss of tissue, symptoms of glaucoma may not appear until 50% or more of the nerve has been damaged. Unfortunately, once nerve damage has occurred, the loss is permanent. It is thus important to find these patients in the asymptomatic stage.
One common type of glaucoma is known as low tension glaucoma. Low tension glaucoma is a special, although common, type of nerve damage that demonstrates the characteristic cupping but does not have the measurable elevation of intraocular pressure that is associated with typical glaucoma. Accordingly, when the eye pressure is measured during clinic visits, it generally falls within the statistically normal range of between 10 and 22 mm Hg. Low pressure glaucoma has long baffled eye care professionals and has accordingly been the subject of much research. In particular, these investigations have evaluated how the eye damage occurs when the intraocular pressure appears normal. Emergent theories range from vascular insufficiency to the optic nerve to a peculiar susceptibility to even "normal" pressures.
It has been estimated that approximately 50% of all new cases of glaucoma can be characterized as low tension glaucoma. The failure of eye care professionals in the past to recognize that this glaucoma can occur even though intraocular pressure appears normal has led to blindness in countless people. Fortunately, modern medical practitioners are more aware and will generally diagnose the problem accurately.
The treatment of glaucoma generally involves lowering the pressure within the eye and thus relieving the nerve. Theoretically, this reduction in pressure will halt or slow the damage of the nerve fibers and hopefully slow or stop the loss of visual field and function.
The treatment modalities for high pressure and low tension glaucoma include: drugs (either topical eye drops or oral medications); laser therapy; or surgical procedures. While all of these methods have been useful in the treatment of high pressure glaucoma, total success has been elusive. This is partially due to the fact that progression of the nerve damage may continue despite what appears to be "successful" reduction of the intraocular pressure. With respect to the treatment of low tension glaucoma, the results have been even more disappointing.
Accordingly, there is a need for an improved method and apparatus for treating disorders of the eye resulting from elevated intraocular pressure.